So ... First things first : UEFI boots, but not in 15kHz yet. That's a big task I'll focus on someday. Then : why not use the june iso ? There are a few things worth the download. Still regarding UEFI and NVMe : it seems some mobos allow booting in legacy mode on NVMe drives, but that's not the case for most of them. So yes, you're probably stuck to a SSD for now.
Then : GA uses 3 partitions. One for boot, one for swap, one for the OS. I'm surprised /boot is empty, as it's a mountpoint of one of the 3 partitions. Can you give me the output of blkid ?
Finally, boot options are set in /boot/syslinux/syslinux.cfg. your trick is only valid from the iso, commenting the archisobasedir shouldn't work, it's a variable that is required for the system to boot.